Submitted to: International Journal of Phytoremediation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2012
Publication Date: 10/31/2012
Publication URL: doi: 10.1080/15226514.2012.702806
Citation: Cabello-Conejo, M.I., Centofanti, T., Kidd, P.S., Prieto-Fernandez, A., Chaney, R.L. 2012. Evaluation of plant growth regulators to increase Ni phytoextraction by Alyssum species. International Journal of Phytoremediation. 15(4):365-375. Interpretive Summary: Rare nickel hyperacculating plant species may be used for phytomining soil nickel, a new technology to obtain nickel from soils and low grade ores which cannot be used for traditional mining and smelting. Such plants can be grown on nickel contaminated soils or natural nickel rich serpentine soils which are extensive in many nations. Some of these plants can accumulate over 2% nickel in shoots under optimum conditions and improved cultivars of the hyperaccumulator plants have accumulated over 3% nickel in Oregon fields. A n earlier short-term greenhouse study suggested that Alyssum murale sprayed with cytokinin had higher biomass yield with no reduction in shoot nickel concentration, which increased the value of a phytomining crop. Because the test used only one plant hormone product and was of short duration, a longer term study was conducted with four Alyssum nickel hyperaccumulator species, three spray concentrations of two commercial hormone formulations. In this test, neither Cytokin or Promalin at any of the tested application rates caused a significant increase in shoot nickel concentration or amount, in any of the tested species. A small but insignificant increase in shoot Ni was observed with Alyssum corsicum, suggesting that under some conditions, a plant hormone response may occur. Other studies remain needed to learn if other commercial plant hormone products could stimulate Ni phytomining potential of hyperaccumulator species.
Technical Abstract: Recent studies have shown that application of phytohormones to shoots of Alyssum murale increased biomass production but did not increase Ni shoot concentration. Increased biomass and Ni phytoextraction efficiency is useful to achieve economically viable phytomining. The objective of this study was to evaluate the effect of two types of phytohormones on the Ni phytoextraction capacity of four Alyssum species. Two different commercially available phytohormones (Cytokin® and Promalin®) based on cytokinins and/or gibberellins were applied at two concentration rates on shoot biomass of four Ni hyperaccumulating Alyssum species (A. corsicum, A. malacitanum, A. murale and A. pintodasilvae). The application of phytohormones had no clear positive effect on biomass production, Ni accumulation and Ni phytoextraction effectiveness in Alyssum species. A. malacitanum was the only species in which a significantly negative effect of these treatments was observed (in Ni uptake). A positive response to promalin treatment was observed in the biomass production and Ni phytoextraction efficiency of A. corsicum. Although this effect was not significant, it does indicate a potential application of these approaches to improve phytoextraction ability. Further studies will be needed to identify the most adequate phytohormone treatment as well as the appropriate concentrations and application times.